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- Path: sparky!uunet!crdgw1!rpi!gatech!destroyer!ncar!noao!arizona!naucse!kendrick.cse.nau.edu
- From: jdc@kendrick.cse.nau.edu (John Campbell)
- Newsgroups: comp.graphics.gnuplot
- Subject: Re: splot/parametric
- Message-ID: <6294@naucse.cse.nau.edu>
- Date: 10 Jan 93 15:47:26 GMT
- References: <1iknkuINNknd@early-bird.think.com>
- Sender: news@naucse.cse.nau.edu
- Lines: 40
- Nntp-Posting-Host: kendrick.cse.nau.edu
- Originator: jdc@kendrick.cse.nau.edu
-
- From article <1iknkuINNknd@early-bird.think.com>, by dkramer@think.com (David Kramer):
- > I am trying to plot a surface in 3.2, with the data (from a file) in three
- > columns representing x, y and z respectively. I find that when I do
- > "splot", I get an odd flat surface, and the extents of the plot are all
- > wrong. If I "set parametric" and replot, the graph looks correct, with
- > correct extents. The problem is that I need to simultaneously plot a
- > non-parametric function.
- >
- > It seems to me that the graph I get with noparametric set is incorrect,
- > and that this is a bug in gnuplot. Has anyone else had similar
- > problems?
- >
- > Thanks
- > David
-
- I'm not sure, but I seem to remember some comments that splot data
- processing worked as expected in parametric mode only. Hopefully someone
- else will clarify this.
-
- However, any function (z=f(x,y)) that you want to plot can easily be
- written in parametric mode (z=x(t),y(t)). The translation is simple.
-
- Consider splot cos(x)/sin(y), in parametric mode, this would be
- u,v,cos(u)/sin(v). In other words, you have x(u,v),y(v,v),z(u,v) as
- three independent tuples to define a single relation. Functions are
- special cases of the more general parametric relations and map
- as follows: f(x,y) = u,v,f(u,v). In other words, there is no such
- thing as a "non-parametric function."
-
- In reviewing this, I guess it should be in the FAQ. I believe, but
- am not sure, that 3d data files are of two forms--and the most natural
- form is where each (x,y,z) column is considered independent of the
- others. Possibly this is why you must specify parametric mode. I'm
- not sure what the non-parametric data file plotting mode means. Someone
- should post a follow-up and add it to the FAQ as well.
-
- PS How's the FAQ coming along these days?
- --
- John Campbell John.Campbell@nau.edu
- jdc@sunset.cse.nau.edu JDC@NAUVAX.UCC.NAU.EDU
-